Kinetics and isotherm studies for the adsorption of metal ions onto two soil types

•Organic Carbon and Cation Exchange Capacity (CEC) influenced the equilibrium time.•Removal rate of Cu(II) by red soil was 97.4% and of Ni(II) by black soil was 99.9%.•Freundlich isotherm model best explained the adsorption process.

Transport of contaminants from soil to other trophic levels is associated with retention/binding capacity of soil with pollutants. The sorption potential of red and black soils for Cu(II) and Ni(II), respectively was analysed through batch experiments. The batch experiments were conducted to identify equilibrium time, equilibrium adsorbent dosage and equilibrium metal concentration. The kinetics and adsorption isotherms were studied using pseudo-first order and pseudo-second order equation, and Langmuir, Freundlich and Temkin isotherm models. Agitation time, adsorbent dosage and metal concentration played a significant role in the rate of adsorption. The percentage removal of Cu(II) and Ni(II) was higher initially and reached equilibrium after 480 min and 300 min of agitation, respectively. The maximum removal rate for Cu(II) by red soil was 97.3% and for Ni(II) by black soil was 99.9%. The examination of kinetics and adsorption isotherm revealed that the sorption experiments fitted well with the pseudo-second order equation and Freundlich isotherm model, respectively. Thus, red and black soil have significant metal retention potential for Cu(II) and Ni(II), respectively.